The method of the invention is accordingly usable in automated transmissions in connection with automated clutch and transmission functions which are used in motor vehicles. Such an automated transmission comprises activation devices for the selection of transmission selection pathways and of transmission shift pathways with which a shifting or selecting lever activation can be converted into corresponding shifting or selection processes in reference to the transmission.
Moreover, an additional activation device for a shifting and starting clutch connected through drive engineering with the transmission is provided, which is placed into operation with gearshifting processes for opening and closing the clutch. The activation devices mentioned are constructed such that these can be activated hydraulically, pneumatically or electrically.
Furthermore, a sensor for determining the clutch position or the clutch adjustment path is arranged on such a clutch or activation device with which the position or the adjustment path of the movable part of the clutch and/or clutch activation device can be ascertained.
Finally, such a transmission comprises an electronic control or regulation apparatus that is usually constructed as a microcomputer and is connected with the sensors and activating equipment mentioned above through sensor and control lines and can preferably perform exchange data with a motor control apparatus.
Above all, automated transmissions offer good shifting comfort, if the control and regulation apparatus knows exactly the clutch position in which the clutch is brought into a closing position such that torque transmission is just setting in.
This clutch position, or a clutch position with a previously established distance from the aforementioned position, is designated as a contact point below. This clutch position can shift in the short or the long term by thermal expansion of the clutch components or by wear and tear of the clutch linings. It is, therefore, necessary to continuously monitor the contact point during operation, especially during the lifetime of the clutch or the motor vehicle and, if need be, to adapt the clutch control in harmony with the changes.
A large number of proposals exist for determining the contact point. In further observations in connection with the present invention, methods in which a transmission input rotational speed sensor is needed will not be considered, since such sensors measuring a drive motor-related variable are to be dispensed with in accordance with the specifications in connection with the invention.
For example, the method described in DE 196 30 014 A1 manages without a transmission input rotational speed sensor of this type. In this known method, the point of contact is determined by applying the clutch when the gear step is shifted and the motor vehicle is standing still while the brake is activated by observing the motor rotational speed. The motor rotational speed is reduced by closing the clutch, resulting in a significant increase in motor torque controlled by an idling rotational speed regulating unit. When the clutch is closed, the position point at which the motor torque exceeds a predefined threshold value of the motor torque, is then recognized as the point of contact and stored in a control apparatus.
Moreover a method is known from WO 01/98679 A1 in which a creep torque is generated by slowly closing the clutch. The motor torque is continuously monitored for this during the creep process. The clutch position point is then determined as the current point of contact at which a significant change in motor torque is observed.
These known methods are based upon sensor signals, which are related to the drive motor of the motor vehicle. These methods are therewith dependent upon the accuracy of these signals which, in practice, leads to unsatisfying results. It is rather desirable if the determination of the contact point can take place with clutch or transmission-related variables.
The object of the invention is, therefore, to ascertain this point without motor-related sensor information for improving the accuracy of determining the contact point of the clutch.
The solution of this objective becomes apparent from the main claim, while advantageous refinements and further developments of the invention can be inferred from the dependent claims.